/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.sedona.core.knnJudgement;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.apache.spark.api.java.function.FlatMapFunction;
import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.index.SpatialIndex;
import org.locationtech.jts.index.strtree.GeometryItemDistance;
import org.locationtech.jts.index.strtree.STRtree;

// TODO: Auto-generated Javadoc

/** The Class KnnJudgementUsingIndex. */
public class KnnJudgementUsingIndex<U extends Geometry, T extends Geometry>
    implements FlatMapFunction<Iterator<SpatialIndex>, T>, Serializable {

  /** The k. */
  int k;

  /** The query center. */
  U queryCenter;

  /**
   * Instantiates a new knn judgement using index.
   *
   * @param queryCenter the query center
   * @param k the k
   */
  public KnnJudgementUsingIndex(U queryCenter, int k) {
    this.queryCenter = queryCenter;
    this.k = k;
  }

  /* (non-Javadoc)
   * @see org.apache.spark.api.java.function.FlatMapFunction#call(java.lang.Object)
   */
  @Override
  public Iterator<T> call(Iterator<SpatialIndex> treeIndexes) throws Exception {
    SpatialIndex treeIndex = treeIndexes.next();
    final Object[] localK;
    if (treeIndex instanceof STRtree) {
      localK =
          ((STRtree) treeIndex)
              .nearestNeighbour(
                  queryCenter.getEnvelopeInternal(), queryCenter, new GeometryItemDistance(), k);
    } else {
      throw new Exception(
          "[KnnJudgementUsingIndex][Call] QuadTree index doesn't support KNN search.");
    }
    List<T> result = new ArrayList();
    for (int i = 0; i < localK.length; i++) {
      result.add((T) localK[i]);
    }
    return result.iterator();
  }
}
